Power transmission



Oct. 24, 1961 INVENTOR. THEODORE VAN METER ATTORNEYS 3,005,463 7 POWER TRANSMISSION Theodore Van Meter, Birmingham, Mich., assignor to Vlckers Incorporated, Detroit, Mich., a corporation of Michigan Filed July 24, 1957, Ser. No. 673,834 3 Claims. (Cl. 137-117) This invention relates to power transmissions, and is particularly applicable to those of the type comprising two .or more fluid pressure energy translating devices, one of which may function as a pump and another as a fluid motor.

This invention is more particularly concerned with a system wherein two or more fluid motors of varying requirements may be operated from a single fluid source and particularly to systems wherein one fluid motor has precedence over the other in receiving its normal requirements of operating fiuid.

Previous systems of this type have required costly and highly critical valving. This invention has overcome the objections by utilizing a simple, conventional flow control valve placed between the source and the primary load and asecond control valve responsive to the pressure drop in the first conduit, thereby providing a low cost and efficient system. I p

. This invention is particularly adaptedfor use in an automatic hydraulic system wherein a constant supply is required, such as for operation of a power steering booster, while a secondary supply is also needed for the operation of, for example, brakes, windows, doors, and seats.

This invention is especially well adapted for use when continuous operation of only a single motor is required, and where excess power may be stored in an accumulator to permit intermittent operation of other motors, even when the entire pump output is being diverted to the first motor.

An object of this invention is to deliver a constant quantity of fluid to a primary circuit for actuation of a fluid motor regardless of the demand in the secondary circuit. e

Another object of this invention is to have one source of supply which can actuate two or more fluid motors of varying requirements.

A still further object is to provide a'sirnple, low cost,

hydraulic circuit with appropriate valving for causing the desired operation to automaticallytake place.

Further objects and advantages of the present invention will be apparent'from the following description,

reference being had to the accompanying drawing wherein a preferred form of the present invention is clearly shown.

In the drawing:

The single figure is a diagrammatic view of a hydraulic system incorporating the present invention.

Referring to the drawing, the system includes a reservoir 10, a pump 12 driven by a variable speed prime mover, not shown, such as a power take-01f from the vehicle engine, and relief valve 14, all of conventional construction. Additional conventional components in the circuit include an unloading valve 16, an accumulator 18, and an open-center steering booster 20. Steering booster 20 may be of the type disclosed in US. Patent No. 2,022,698 to Harry F. Vickers. Such steering boosters require a substantially constant rate of fluid supply for proper operation.

Fluid from pump 12 is supplied to steering booster 20 through a primary circuit which includes a conduit 22, meter-in flow control -vlve generally designated 24, and a conduit 26.

The unloading valve 16 and the accumulator 18 are supplied with fluid from the pump 12 through a secondary States Patent circuit which includes a conduit 28, a differential-pressure responsive flow control valve generally designated 30, and a conduit 32.

The unloading valve 16 is of the conventional type which is responsive to pressure conditions in the accumulator circuit. When the accumulator is fully charged, unloading valve 16 will divert fluid from conduit 32 back to reservoir 10 through a conduit 34. When the accumulator pressure is low, unloading valve 16 will direct fluid from conduit 32 through the conduit 36 to recharge the accumulator, and to provide fluid for intermittently operated motors, not shown, which are connected to the conduit 36 beyond the point 38.

The valve 24 includes a valve bore 40 halving a spool 42 slidably mounted therein. Spool 42 is biased to the left in the figure by a spring 44. The spool 42' divides the bore 40 into a pair of pressure chambers 46 and 48, and presents equal and opposed areas to the pressures in those two chambers. A metering orifice 50 in spool 42 effects communication between chambers 46 and 48. The bore 40 includes an annulus 52 which communicates with conduit 26 and, in the spring biased position of spool 42, is in open communication with the pressure chamber 48. Valve 24 is of the type termed normally open in that it is initially biased to the open position and is shiftable toward its closed position as it performs its control function.

.By way of example, spring '44 may be so selected that 'a pressure differential of 15 p.s.i. between chambers 46 and 48 will cause the spool 42 to shift rightwardly'to restrict communication between annulus 52 and chamber 48. The orifice 50 is of a size such that a 15 psi. pressure drop across it would provide the maximum desired flow to the booster 20, for example 2 gallons per minute.

The pressure-differential responsive flow control valve 30 includes a valve bore 54 having a valve spool 56 slidably mounted therein. Spool 5'6 divides the valve bore 54 into a pair of chambers 5'7 and 58 and presents equal and opposed areas to the pressures in those chambers. A

spring 60 normally biases the valve spool 56 to the leftward position illustrated, wherein it blocks communicai a conduit 64 with the primary circuit at a point "downstream of valve 24. Spring60- is so selected as to require a greater pressure differential between chambers 57 and 58 in order to shift spool 56 than is required between chambers 46 and 48 to shift spool 42. By way of example, we have previously indicated that a 15 p.s.i. diflerential is required to shift spool 42, and thus spring 60 might be selected to require a 20 p.s.i. pressure differential between chambers 57 and 58 to shift spool 56.

In operation, assume that with the vehicle engine idling the output of pump 12 is something less than 2 gallons per minute. Under these conditions, all the fluid pumped will pass through the primary circuit to the steering booster since a flow rate of 2 gallons per mintue is necessary before a 15 p.s.i. pressure differential is created across the orifice 50, and a 15 p.s.i. pressure differential is required before spool 42 will shift to restrict communication between chamber 48 and the annulus 52. No fluid will be supplied to the secondary circuit since valve 56 will remain closed due to the pressure differential between chambers 57 and 58 being less than the 20 p.s.i. required to compress spring 60.

When the vehicle engine speed is increased to a point where the output of pump 12 exceeds 2 gallons per minute, the pressure diflerential between chambers 46 and 48 will tend to exceed psi. causing spool 42 to shift rightwardly, restricting communication between chamber 48 and annulus 52, thus limiting flow in the primary circuit. The additional restriction to flow in the primary circuit introduced by the shifting of spool 42 will create a pressure drop between primary circuit conduits 22 and 26 which is in excess of the p.s.i. required to shift spool 56. This differential is imposed across spool 56 of valve 30, causing it to shift and open communication between conduits 28 and 32 of the secondary circuit. Thus, any output of pump 12 in excess of 2 gallons per minute will be available to the secondary circuit for use in charging accumulator 18, when needed. In the event that accumulator 18 is fully charged, the excess fiuid is returned to reservoir 10 through conduit 34 at minimum pressure, thus conserving power.

It should be noted that when the pump output exceeds 2 gallons per minute, in the cited example, pump outlet pressure is dictated by whichever circuit has the higher pressure requirement at any given time. However, during the lengthy intervals of no demand in the secondary circuit, the usually low pressure requirement of the steering booster is the controlling factor. It will be seen from the foregoing that there has been provided an efiicient, low cost system for supplying a plurality of fluid motors having varying requirements from a single source.

While the form of embodiment of the invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. In a hydraulic power transmission for controlling the division of flow from a single source, the combination of: primary and secondary circuits; a first delivery conduit leading to said primary circuit and a second delivery conduit leading to said secondary circuit, said conduits having a point of common communication with said source; an orifice in said first conduit; and a pair of separately shiftable valves for regulating the flow between said circuits comprising, a first flow control valve in said first conduit having means to normally bias said valve to an open position and having opposed areas connected respectively to points upstream and downstream of said orifice so as to be shiftable in response to a predetermined pressure drop across said orifice to restrict said first conduit, and a second flow control valve in said second conduit having means to normally bias said second valve to a closed position and having opposed areas connected respectively to points in said first conduit upstream and down stream of said first valve so as to be shiftable in response to the pressure drop created by the shifting of said first valve, thereby opening said second conduit only after said first valve has shifted to restrict said first conduit.

2. In a hydraulic power transmission for controlling the division of flow from a single source, the combination of: primary and secondary circuits; a first delivery conduit leading to said primary circuit and a second delivery conduit leading to said secondary circuit, said conduits having a point of common communication with said source; an orifice in said first conduit; and a pair of separately shiftable valves for regulating the flow between said circuits comprising, a first flow control valve in said first conduit having means to normally bias said valve to an open position and having opposed areas connected respectively to points upstream and downstream of said orifice so as to be shiftable in response to a predetermined pressure drop across said orifice to restrict said first conduit, and a second flow control valve in said second conduit having means to bias said second valve to a closed position and having opposed areas connected respectively to points in said first conduit upstream and downstream of both said orifice and said first valve so as to be shiftable in response to a predetermined pressure drop across both said orifice and said first valve to open said second conduit.

3. In a hydraulic power transmission for controlling the division of flow from a single source, the combination of: primary and secondary circuits; an accumulator and unloading valve in said secondary circuit; a first delivery conduit leading to said primary circuit and a second delivery conduit leading to said secondary circuit, said conduits having a point of common communication with said source; an orifice in said first conduit; and a pair of separately shiftable valves for regulating the flow between said circuits comprising, a first flow control valve in said first conduit having means to normally bias said valve to an open position and having opposed areas connected respectively to points upstream and downstream of said orifice so as to be shiftable in response to a predetermined pressure drop across said orifice to restrict said .first conduit, and a second flow control valve in said second conduit having means to normally bias said second valve to a closed position and halving opposed areas connected respectively to points in said first conduit upstream and downstream of said first valve so as to be shiftable in response to the pressure drop created by the shifting of said first valve, thereby opening said second conduit only after said first valve has shifted to restrict said first conduit.

References Cited in the file of this patent UNITED STATES PATENTS 2,462,983 MacDuff et al Mar. 1, 1949 2,594,689 Sharp Apr. 29, 1952 2,737,196 Eames Mar. 6, 1956 2,818,711 Lincoln Jan. 7, 1958 

